There are many situations where one wishes to modulate cellular growth. Since all of life is dependent upon cellular regeneration, there is substantial interest in being able to modulate cellular growth in the plant and animal kingdoms. In the case of plants, one wishes to encourage the growth of desirable plants, such as plant crops and flowers, while at the same time one wishes to discourage the growth of weeds, both pre-germination and post-germination of the desired plant. In many situations one wishes to kill all vegetation, such as highway borders, pathways, graveled areas, and the like. However, many of the herbicides which are used today pollute the environment in introducing undesirable elements into the soil, which can then be leached into aquifers, streams and rivers. There is, therefore, substantial interest in being able to reduce the amount of herbicidal use without further pollution of the environment.
There is also the need to root stock to expand desired plants, particularly woody stock. Better methods are needed to increase the efficiency and reduce the time for rooting.
Finally, there is the proliferation of cells in the animal kingdom. The development of the various species from a single fertilized cell to the mature adult requires rapid proliferation. However, during the life of the organism, there are many situations where rapid proliferation is undesirable. Various diseases associated with rapid proliferation include cancers, psoriasis, restenosis, and the like. Many of the agents used for treating these diseases, are cytotoxic agents which attack all proliferating cells and frequently have substantial side effects in addition to their cytotoxic activity.
Various techniques have been employed to reduce the systemic influences of these cytotoxic drugs. Immunotoxins employ a toxin joined to an antibody, where the antibody is specific to varying degrees for a marker present on cancer cells. Another technique which is limited to physical access to the tumor employs the cytotoxic drug in a matrix which reduces the translocation of the cytotoxic drug from the site of the lesion. Other techniques have involved use of liposomes with agents, such as antibodies, to direct the liposomes to the target, where the lumen of the liposome comprises a cytotoxic agent. However, none of these techniques has found universal acceptance. So long as one continues to use the cytotoxic drugs in systemic fashion, there is substantial interest in finding ways to diminish the amount required for an effective dosage as a cytotoxic agent.